Fuel injection system

ABSTRACT

A fuel injection system ( 1 ) for an internal combustion engine ( 1′ ) includes a fuel injector ( 4 ) which injects fuel into a combustion chamber ( 7 ) delimited by a cylinder wall ( 14 ) in which a piston ( 6 ) is guided, and having a spark plug ( 3 ) projecting into the combustion chamber ( 7 ), the fuel injector ( 4 ) producing multiple injection jets ( 10 ) in the combustion chamber ( 7 ). At least one gap ( 15 ) is provided in the injection jets ( 10 ) in an area remote from the spark plug ( 3 ).

BACKGROUND INFORMATION

[0001] The present invention relates to a fuel injection system according to the definition of the species of the main claim.

[0002] In internal combustion engines having spark ignition of a compressed fuel mixture with internal formation of the mixture, a “mixture cloud” which must have a certain fuel-air ratio in the ignitable range is required in the area of the spark plug for stratified charge operation. To this end, fuel injectors having nozzles which open toward the inside or the outside and produce a conical jet are used.

[0003] For example, German Patent Application 198 04 463 A1 describes a fuel injection system for internal combustion engines having spark ignition of a compressed fuel mixture; this fuel injection system is provided with at least one fuel injector which injects fuel into a combustion chamber formed by a piston/cylinder arrangement and is equipped with a spark plug projecting into the combustion chamber. The nozzle body of the fuel injector is provided with at least one row of injection holes distributed over the circumference of a nozzle body of the fuel injector. Through controlled injection of fuel through the injection holes, a jet-guided combustion method is implemented by the formation of a mixture cloud, at least one jet being directed in the direction of the spark plug. Other jets ensure that an at least approximately closed, i.e., contiguous mixture cloud is formed.

[0004] German Patent 196 42 653 C1 describes a method of forming an ignitable fuel-air mixture. An ignitable fuel-air mixture is formable in the cylinders of direct-injection internal combustion engines, in that fuel is injected into each combustion chamber delimited by a piston, by way of an injector on opening of a nozzle orifice due to a valve element being lifted up from a valve seat surrounding the nozzle orifice. To permit formation of an internal mixture optimized for fuel consumption and emissions at each operating point of the entire engine characteristics map under all operating conditions of the internal combustion engine, in particular in stratified charge operation, the opening stroke of the valve element and the injection time are adjustable.

[0005] German Patent 38 08 635 C2 describes a fuel injection device for direct injection of fuel into the cylinder of an internal combustion engine having compression of a fuel mixture. The fuel injection device includes a fuel injector which is situated in the cylinder wall at a distance from the cylinder head and opposite the exhaust opening and which has an outlet opening, with the axis of the jet of the injection valve being directed at the area around the spark plug situated in the cylinder head. The fuel injector here has a magnetically operated valve needle having helical swirl grooves to produce a swirl flow of the injection jet. The total cross-sectional area of the swirl grooves is smaller by at least one half than the cross-sectional area of the outlet opening, the fuel injector being situated above a flushing opening, and with its jet axis directed at the ignition point situated at the center of the cylinder head.

[0006] Air-guided or wall-guided combustion methods are implemented with the injection systems known from the publications cited above. The air-guided combustion method depends to a very great extent on the movement of incoming air, which has the function of conveying an ignitable fuel-air mixture exactly into the electrode area of the spark plug over the entire stratified charge operation range of the engine characteristics map. In the wall-guided combustion method, fuel is carried to the spark plug with the support of more or less fractured combustion chamber geometries with simultaneous formation of the mixture.

[0007] Transport of the mixture to the spark plug is very incomplete in wall-guided and air-guided combustion methods in idling operation and in the lower partial load range; in the middle partial load range of operation, it is possible in part only with unjustifiably low manufacturing tolerances of the high-pressure injectors used or the flow guidance through the intake manifold. The inadequate reproducibility is apparent in particular in increased emission of unburned hydrocarbons due to isolated instances of misfiring.

[0008] On the other hand, the jet-guided-combustion method is usable only above a certain cylinder stroke volume, which is approximately 500 cm³. In today's related art, a certain minimum size is required for the hole diameter of the injection holes for technical reasons, so the arrangements described above result in an overly rich mixture in the case of small cylinder stroke volumes. This results in inferior emission values and higher fuel consumption. The lower limit for the hole diameter is currently approximately 0.12 mm. The injection holes are created by the erosion method. The fuel volume injected can be reduced only by decreasing the number of injection holes, but then the geometry of the fuel jet may become less favorable for the flammability of the fuel-air mixture. Therefore, the fuel jet is aimed at the spark plug in these cases.

[0009] Advantages of the Invention

[0010] The fuel injection system according to the present invention having the characterizing features of the main claim has the advantage over the related art that due to the fact that an area remote from the spark plug is left out in injection, the quantity of fuel injected can be reduced by decreasing the number of injection holes without having to reduce the diameter of the injection holes. Thus the requirements of a lower fuel demand of internal combustion engines having a small stroke can be taken into account without requiring complicated measures for introducing smaller injection holes into the fuel injector.

[0011] Advantageous refinements of the fuel injection system characterized in the main claim are possible through the measures characterized in the subclaims.

[0012] In particular, the thermal shock load and sooting of the spark plug are reduced by tangential injection of fuel with respect to the position of the spark plug, so the spray jets are not aimed directly at the spark plug.

[0013] It is also advantageous that the gap in the jet at the spark plug opens up the possibility of igniting the fuel-air mixture during injection in all areas of the engine characteristics map and in all operating ranges of the internal combustion engine or to inject fuel during ignition.

[0014] Through a specific combination of the injection holes and thus the injection jets in the combustion chamber, the installed position of the intake and exhaust valves as well as of the spark plug in the cylinder head may also be taken into account to advantage, and the geometry of the combustion chamber depression in the piston can be utilized optimally.

[0015] Fuel injectors suitable for the fuel injection system may be manufactured inexpensively to advantage without requiring any additional manufacturing measures. In addition, sensitivity to the mounting depth of the spark plug decreases due to the possible larger diameter of the injection holes.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Embodiments of the present invention are illustrated in simplified form in the drawing and are explained in greater detail in the following description.

[0017]FIG. 1 shows a schematic section through a fuel injection system according to the related art for a jet-guided combustion method,

[0018]FIG. 2 shows a schematic section through a first embodiment of the fuel injection system according to the present invention, along line II-II in FIG. 1,

[0019]FIG. 3 shows a schematic section through a second embodiment of the fuel injection system according to the present invention, along line II-II in FIG. 1,

[0020]FIG. 4 shows a schematic section through a third embodiment of the fuel injection system according to the present invention, along line II-II in FIG. 1,

[0021]FIG. 5 shows a schematic section through a fourth embodiment of the fuel injection system according to the present invention, along line II-II in FIG. 1, and

[0022]FIG. 6 shows a schematic section through a fifth embodiment of the fuel injection system according to the present invention, along line II-II in FIG. 1.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023]FIG. 1 shows a detail of a schematic sectional diagram of a longitudinal section through a cylinder of an internal combustion engine 1′ having one or more cylinders, operating by compression of a fuel mixture. Internal combustion engine 1′ has a cylinder head 2 in which there are situated a spark plug 3 and a fuel injector 4 in suitably designed recesses.

[0024] Since the design of both spark plug 3 and fuel injector 4 are known, these parts need not be described further here. The detail of internal combustion engine 1′ illustrated in FIG. 1 is referred to below as fuel injection system 1.

[0025] Fuel injector 4 injects fuel in a partially closed injection cone 5 into a combustion chamber 7 delimited by cylinder head 2, a piston 6 and a cylinder wall 14 which is indicated only schematically. Combustion chamber 7 is formed in part by a combustion chamber depression 8 formed in piston 6.

[0026] Fuel injector 4 and spark plug 3 are situated relative to one another so that spark plug 3 projects into combustion chamber 7 at a lateral offset from-fuel injector 4, spark plug electrodes 9 being situated in the area of injection cone 5.

[0027] The shape of injection cone 5 depends on the design of the spray end of fuel injector 4. Fuel injector 4 is expediently designed as an inwardly opening fuel injector 4 (I valve). Fuel is injected into combustion chamber 7 by energizing a magnetic or piezoelectric actuator, causing a valve needle (not shown) or a valve closing body connected to it to lift up from a valve body equipped with injection holes. Fuel is thus injected into combustion chamber 7 through fuel injector 4 and the injection holes in the valve body.

[0028]FIGS. 2 through 6 each show in a detail of a sectional diagram a section through cylinder head 2 of internal combustion engine 1′ having fuel injection system 1 as illustrated in FIG. 1. The section runs along line II-II in FIG. 1. This shows a view of the upper end of piston 6, combustion chamber depression 8 formed there, delimited by edge 11 of the combustion chamber depression shown with broken lines, each figure showing different embodiments of the arrangement of fuel injector 4, spark plug 3, injection jets 10 and a variable number of intake valves 12 and exhaust valves 13.

[0029] Injection jets 10 are shown as lines in an idealized form. In reality, injection jets 10 have a certain spatial extent, so that adjacent injection jets 10 situated side by side at an angle β are in mutual contact and form a conical segment-shaped spray geometry in these areas. This partially conical spray pattern is interrupted in the gaps at spark plug 3 or spark plugs 3 a, 3 b (i.e., in angular areas a) as well as in gaps 15 according to the present invention.

[0030]FIG. 2 shows a first embodiment of displacement volumes of less than 500 cm³, fuel injector 4 injecting two injection jets 10 into combustion chamber 7 tangentially to spark plug 3. Vertex angle a preferably amounts to approximately 45°.

[0031] Combustion chamber depression edge 11 is designed according to the arrangement of two injection jets 10 to support the combustion. The angle recess or gap 15 of injection jets 10 behind spark plug 3 thus amounts to approximately 315°. Two intake valves 12 are also arranged in this area. Two exhaust valves 13 may be situated in the injection direction. The arrangement of intake and exhaust valves 12, 13 may also be reversed or otherwise different.

[0032]FIG. 3 shows a second embodiment of fuel injection system 1 according to the present invention. A total of four injection jets 10 are injected into combustion chamber 7 by fuel injector 4. Inner injection jets 10 a are situated approximately tangentially to spark plug 3, and outer injection jets lob are situated at an angular distance β of 20° to 30° to inner injection jets 10 a. Combustion chamber depression edge 11 is again adapted to the arrangement of injection jets 10. In this embodiment, intake and exhaust valves 12 and 13 are situated in other areas of cylinder head 2. The arrangement of four injection jets 10 is suitable for somewhat larger displacement volumes for which somewhat more fuel is needed than in the first embodiment. The angle gap not covered by injection jets 10 in the area of gap 15 opposite spark plug 3 amounts to between 250° and 280° in this embodiment.

[0033]FIG. 4 shows a third embodiment of an internal combustion engine 1′ having a further increase in displacement, the number of injection jets 10 now being eight. As in the previous embodiments, inner injection jets 10 a are situated approximately tangentially to spark plug 3, angle a between them being approximately 45°. Outer injection jets lob are each arranged at angular distances β of 20° to 30° to inner injection jets 10 a. The angle not covered by injection jets 10 in the area of gap 15 opposite spark plug 3 is between 130° and 200° in the present embodiment. Combustion chamber depression-edge 11 is again adapted to the jet pattern. An intake valve 12 and an exhaust valve 13 may be provided symmetrically with a line on which fuel injector 4 and spark plug 3 are situated.

[0034]FIG. 5 and FIG. 6 illustrate preferred variants of the embodiments for fuel injection systems 1 having at least two spark plugs 3 a, 3 b.

[0035] In the same type of diagram as that in FIGS. 2 through 4, FIG. 5 illustrates a fourth embodiment of a fuel injection system 1 which has two spark plugs 3 a and 3 b which are situated symmetrically with fuel injector 4. An intake valve 12 and an exhaust valve 13 are situated so that spark plugs 3 a and 3 b as well as intake valve 12 and exhaust valve 13 form a cloverleaf arrangement. For small-displacement internal combustion engines 1′, it is possible to implement an arrangement having four injection jets 10 which are injected into combustion chamber 7 at an angle α of approximately 45° to one another, approximately tangentially to spark plugs 3 a and 3 b. For somewhat larger displacement volumes, it is possible to inject a total of eight injection jets 10 which preferably cover the interspaces between intake and exhaust valves 12, 13 and two spark plugs 3 a, 3 b. Combustion chamber depression edge 11 is designed to be circular in this embodiment. Two injection jets 10 c are injected approximately tangentially to first spark plug 3 a, and two other injection jets 10 d are injected approximately tangentially to second spark plug 3 b as inner injection jets 10 c, 10 d. Four outer injection jets 10 e are injected at an angular distance β from inner injection jets 10 c, 10 d. FIG. 6 shows a fifth embodiment of fuel injection system 1 according to the present invention, two intake valves 12 being arranged here opposite an exhaust valve 13. Combustion chamber depression edge 11 is again designed to be circular. Spark plugs 3 a and 3 b are surrounded approximately tangentially by injection jets 10, their vertex angle a being 45°. For a slightly larger displacement, six injection jets 10 may also be injected into combustion chamber 7, angular distance β between inner injection jets 10 a, which are tangential to spark plugs 3 a, 3 b, and outer injection jets lob, shown with broken lines, may be between 20° and 30°.

[0036] In all embodiments of fuel injection system 1, injection jets 10 are oriented so that one or more gaps 15 are formed, spanning an angular range of at least 150° and at most 315°.

[0037] The present invention is not limited to the embodiments presented here, and it is also applicable for fuel injection systems 1 having fewer or more injection holes 11, intake and exhaust valves and in particular several spark plugs and variable displacements even of less than 500 cm³. In particular, this permits fuel injectors whose cone vertex angle of the injection jets may assume any values between 30° and 150°. 

What is claimed is:
 1. A fuel injection system (1) for an internal combustion engine having at least one fuel injector (4) which injects fuel into a combustion chamber (7) delimited by a cylinder wall (14) in which a piston (6) is guided, and having a spark plug (3) projecting into the combustion chamber (7), the fuel injector (4) producing multiple injection jets (10) in the combustion chamber (7), wherein at least one gap (15) is provided in the injection jets (10) in an area remote from the spark plug (3).
 2. The fuel injection system according to claim 1, wherein injection holes of the fuel injector (4) are-distributed so that at least two injection jets (10) are injected into the combustion chamber (7) tangentially to the spark plug (3) at a predetermined vertex angle (α).
 3. The fuel injection system according to claim 2, wherein the predetermined vertex angle (α) is approximately 45°.
 4. The fuel injection system according to claim 3, wherein a combustion chamber depression (8) situated in one end of the piston (6) is designed so that the injection jets (10) extend in the area of the combustion chamber depression (8).
 5. The fuel injection system according to one of claims 1 through 4, wherein at least four injection jets (10) are injected into the combustion chamber (7), the inner injection jets (10 a) injected tangentially to the spark plug (3) forming a predetermined first angle (α), and outer injection jets (10 b) forming a predetermined second angle (β) with the inner injection jets (10 a).
 6. The fuel injection system according to claim 5, wherein the second angle (β) is between 20° and 30°.
 7. The fuel injection system according to one of claims 1 through 6, wherein at least four injection jets (10) are injected into the combustion chamber (7), two first injection jets (10 c) being injected tangentially to a first spark plug (3 a) and two second injection jets (10 d) being injected tangentially to a second spark plug (3 b), and the first injection jets (10 c) and the second injection jets (10 d) each forming a predetermined first angle (α).
 8. The fuel injection system according to claim 7, wherein at least eight injection jets (10) are injected into the combustion chamber (7) in such a way that a constant angle (β) is formed between the inner injection jets (10 c, 10 d) encompassing the first spark plug (3 a) and the second spark plug (3 b) and additional outer injection jets (10 e). 